Of course companies can purchase insurance coverage and take risk management decisions to ameliorate risk. That’s exactly what companies/organizations that run summer camps, backpacking trips, and travel programs for children and teens do, because they have chosen to cater to that market. That’s the entire point of recommending that the OP look at those kinds of programs.
But if a company offers horse riding trips for adults and families, and does not specifically indicate that they have programs for teens that are not traveling with parents/responsible adults, then they have already chosen the market they want to cater to - and it’s not unaccompanied minors. That’s kind of my point.